The detection of covalent and noncovalent binding events between molecules and biomembranes is a fundamental goal of contemporary biochemistry and analytical chemistry. This detection serves for the basic study of central biological processes like signaling, and for the development of high throughput screening of drug candidates from large libraries of molecules that potentially recognize a specific membrane receptor. Currently, such studies are performed routinely using fluorescence methods (Chattopadhyay and Raghuraman, 2004), surface-plasmon resonance (SPR) spectroscopy (Baciu et al., 2008), and electrochemical methods (Thompson and Krull, 1982; Thompson et al., 1983; Umezawa et al., 1988; Woodhouse et al., 1999; Xu and Bakker, 2009; Dumas et al., 2011; Coldrick et al., 2011). However, there is still need for novel sensitive miniaturizable detection methods, e.g., for point-of-care testing (POCT).
The preparation and characterization of model membranes on solid supports, e.g., semiconductors, is a practical and scientifically important research area (Tanaka and Sackmann, 2005). Practical applications include smart biosensor devices for studying basic membrane processes and membrane-analyte interactions, as well as for other biotechnological applications (Bieri et al., 1999; Sackmann and Tanaka, 2000; Sapuri et al., 2002; Yip et al., 2002).
Recent advances in microelectronics and nanotechnology, improvement in sensor function, and emergence of new types of biosensors have increased the interest in development of lipid membrane-based systems. Electrochemical methods were applied since they allow direct conversion of biological information to electronic signal. They are well suited for investigation of biomembrane functions due to their operation simplicity, low cost, and capability of real-time measurements. Typically, electrochemical biosensors employ amperometric, potentiometric, or impedimetric transducers (Thompson and Krull, 1982; Thompson et al., 1983; Umezawa et al., 1988; Woodhouse et al., 1999; Xu and Bakker, 2009; Dumas et al., 2011; Coldrick et al., 2011).
Sensors based on field-effect transistor (FET) configuration have been utilized since the early 1970s (Bergveld, 1972; Bergveld et al., 1978). This special class of sensors makes use of the potentiometric effect at a gate electrode (Thevenot et al., 2001). Currently, biosensing applications focus on ion-selective FET (ISFET or CHEMFET) devices. In ISFET, the regular gate is placed in a liquid electrolyte, and the diffusion of specific analytes toward the electrode can be controlled by insertion of a selective membrane positioned on the gate. ISFET approach was utilized, e.g., for studying enzyme-substrate recognition and for detecting neurons or living cell activity (Baumann et al., 1999; Kharitonov et al., 2000; Schoning and Poghossian, 2002; Bergveld, 2003; Janata, 2004). A theoretical model for biorecognition of acetylcholine applying enzyme-modified ISFET was provided recently (Goykhman et al., 2009). According to this model, the electrical response of the device, during enzyme-substrate recognition events, depends on cooperative effects of local pH changes and molecular dipole variations.
International Patent Publication No. WO 98/19151 (corresponding to U.S. Pat. No. 6,433,356) of the same applicant of the present invention, herewith incorporated by reference in its entirety as if fully disclosed herein, describes a hybrid organic-inorganic semiconductor device and sensors based thereon, said device characterized by being composed of: (i) at least one layer of a conducting semiconductor; (ii) at least one insulating layer, (iii) a multifunctional organic sensing molecule directly chemisorbed on one of its surfaces, said multifunctional organic sensing molecule having at least one functional group that binds to the said surface of the electronic device, and at least one other functional group that serves as a sensor, and (iv) two conducting pads on the top layer making electrical contact with the electrically conducting layer, such that electrical current can flow between them at a finite distance from the surface of the device. The semiconductor devices disclosed in WO 98/19151 are referred to as molecular controlled semiconductor resistors (MOCSERs) and described as light or chemical sensors.